In recent years there has been a increasing use of positive displacement fluid infusion pumping devices for delivery fluids intravenously or intra arterially to patients in hospitals or other patient care locations. These have to a large extent replaced the time honored gravity flow control systems, primarily due to their much greater accuracy in delivery rates and dosages, the relative sophistication in permitting a flexible and controlled feed from multiple liquid sources, and particularly their ability to control with precision the amount of dangerous drugs delivered to a patient over a given period of time.
A typical positive displacement infusion pump system includes a pump driver device and a disposable cassette. The disposable cassette, which is adapted to be used only for a single patient and for one fluid delivery cycle, is typically a small plastic unit having an inlet and an outlet respectively connected through flexible tubing to the fluid supply container and to the patient receiving the infusion. The cassette includes a pumping chamber with the flow of fluid through the chamber being controlled by a plunger or piston activated in a controlled manner by the driver device. For example, the cassette chamber may have one wall thereof formed by a flexible diaphragm which is reciprocated by the plunger in the driver to cause fluid to flow. The pump driver device includes the plunger or piston for controlling the flow of fluid into and out of the pumping chamber in the cassette, and it also includes control mechanisms to assure that the fluid is delivered to the patient at a pre-set rate, in a pre-determined manner, and only for a particular pre-selected time or total dosage. The pump driver device may also include pressure sensing and other liquid flow monitoring devices as well as valving members for opening and closing various passages in the cassette including the inlet and outlet passages of the pumping chamber.